The current state of the art and future CMOS technology requires sub-50 nm metal contacts for connecting the CMOS devices, such as field effect transistors (FETs), to the back-end-of-line (BEOL) wiring. However, the currently available 0.93 numerical aperture (NA) lithographic tool can only resolve lithographic patterns with contact openings of not less than 100 nm in diameter. Future generation of 1.2 NA lithographic tool is expected to print lithographic patterns with contact openings of about 70 nm to 80 nm in diameter. The large contact opening diameter contributes to an undesirable low device density on the integrated chip.
Therefore, there is a need for reducing the CMOS contact opening diameter to even below the resolutions of the lithographic tools, i.e., there is a need for sub-lithography feature patterning.
It has been known that certain materials are capable of spontaneous organization of materials into ordered patterns without the need for human interference, which is typically referred to as the self-assembly of materials. Examples of material self-assembly range from snowflakes to seashells to sand dunes, all of which form some type of regular or ordered patterns in response to the external conditions.
Among various self-assembling materials, self-assembling block copolymers that are capable of self-organizing into nanometer-scale patterns are particularly promising for enabling future advances in the semiconductor technology. Each self-assembling block copolymer system typically contains two or more different polymeric block components that are immiscible with one another. Under suitable conditions, the two or more immiscible polymeric block components separate into two or more different phases on a nanometer scale and thereby form ordered patterns of isolated nano-sized structural units.
Such ordered patterns of isolated nano-sized structural units formed by the self-assembling block copolymers can be used for fabricating nano-scale structural units in semiconductor, optical, and magnetic devices. Specifically, dimensions of the structural units so formed are typically in the range of 10 to 40 nm, which are sub-lithographic (i.e., below the resolutions of the lithographic tools). Further, the self-assembling block copolymers are compatible with conventional semiconductor, optical, and magnetic processes. Therefore, the ordered patterns of nano-sized structural units formed by such block copolymers have been integrated into semiconductor, optical, and magnetic devices where a large, ordered array of repeating structural units are required.
However, the CMOS technology requires precise placement or registration of individual structural units for formation of metal lines and vias in the wiring levels. Therefore, the large, ordered array of repeating structural units formed by self-assembling block copolymers could not be used in CMOS devices, because of lack of alignment or registration of the position of individual structure unit.